Method for making a reinforced air bag door cover

ABSTRACT

A method is disclosed for forming a reinforced plastic skin for an automobile interior trim structure. The method includes the steps of supplying a plastic material onto a mold surface, heating the plastic material to fuse it into a unitary layer, embedding a reinforcing material into the layer, and cooling the plastic and reinforcing materials. The method can be used to reinforce an air bag door cover by incorporating a tear seam into the plastic layer and embedding the reinforcing material into the layer such that it surrounds the tear seam. The reinforcing material aids in rupturing of the cover along the designated tear seam during deployment of the air bag. Also disclosed is an air bag door cover formed in accordance with the disclosed method.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to automotive interior trim structuresincorporating a cover for an air bag deployment opening and, inparticular, relates to an automobile interior trim structure having adecorative outer skin that includes a reinforced air bag door cover.Further, the invention relates to a method for making the reinforcedouter skin.

2. Description of the Related Art

Various types of supplemental involuntary restraint systems (SIRs) arecurrently being provided by automobile manufacturers to help reduce theextent of personal injuries incurred in automobile accidents. Air bagsare increasingly becoming one of the most common and popular SIRsutilized. Air bags are designed to inflate during a collision torestrain forward movement of the driver and/or other occupants to helpavoid injurious contact with interior portions of the automobile.

Air bags are typically stowed behind one or more interior trimstructures, such as the steering wheel cover, door panel, or passengerside portion of the instrument panel. These interior trim structuresmust, therefore, be specifically manufactured to permit deployment ofthe air bag upon a collision being detected. Such manufacturing entailsconsideration of a multitude of design requirements, such as thefunctional requirements of the air bag deployment system and theaesthetic requirements of the interior trim structures. Moreover, manyof these requirements involve counter-vailing considerations. Forexample, the air bag should be able to be deployed virtuallyinstantaneously upon a collision being detected. However, it should bestowed in such a manner as to 1) inhibit accidental or intentionaltampering that would interfere with its performance and 2) contribute toan overall pleasing interior appearance. In regard to the latterconsideration, it is, as a matter of human psychology, undesirable toremind the automobile occupants of the dangers of driving and theexistence of the air bag is therefore preferably made entirelyinvisible.

Interior trim structures used in automotive applications typicallycomprise a composite article having a foam layer formed between a rigidinsert and a decorative outer skin. The insert provides structuralreinforcement to the interior trim structure and is used to secure thetrim structure within the automobile interior. Because the reinforcinginsert is rigid, it either has an opening through which the air bag isdeployed or is manufactured with one or more hinges which define one ormore doors that open upon the air bag being inflated. The portion of thedecorative outer skin that overlies the air bag deployment opening ishereinafter referred to as the air bag door cover.

In the typical air bag deployment scheme, the air bag forces its way outof its stowed position upon expansion. Various arrangements of theinterior trim structures have been suggested to accommodate deploymentof the air bag in this manner. One such arrangement involves forming theair bag door cover as a unitary part of the outer skin of the interiortrim structure and pre-weakening the air bag door cover on its inside(i.e., non-decorative) surface to form a tear seam along which the outerskin will separate under the force of expansion of the air bag.

The outer skin, and therefore the air bag door cover, is typically madefrom a vinyl material such as a polyvinyl chloride (PVC). At coldtemperatures, this vinyl material becomes brittle, increasing thelikelihood of cracking of the door cover along the tear seam as well asfragmentation of the door cover upon deployment of the air bag.Conversely, at elevated temperatures, the vinyl skin material has asignificantly increased tensile elongation and is therefore moredifficult to rupture. Moreover, such elongation during expansion of theair bag can cause separation of the outer skin from the intermediatefoam layer, possibly resulting in pieces of foam becoming separated fromthe foam layer.

As mentioned above, the interior trim structure, of which the air bagdoor is made a part, typically comprises a foam layer formed between arigid insert and an outer skin. The air bag deployment opening iscovered by an air bag door which can have a structure corresponding tothe remainder of the interior trim structure, i.e., the air bag door cancomprise a foam layer formed between the outer skin and a hinged, rigidbackside which provides reinforcement of the air bag door. Although therigid backside can aid rupturing of the tear seam upon deployment of theair bag, it is not in direct contact with the air bag door cover inwhich the tear seam is formed. Rather, it must act through therelatively soft foam layer which decreases its ability to cause the airbag door cover to separate along its tear seam.

Reinforcing members have been used for various reasons in otherapplications. For example, U.S. Pat. No. 4,455,340, issued Jun. 19, 1984to T. Okina, discloses a flexible molded foam article having anintermediate reinforcing layer located between a semi-rigid polyurethanefoam core and surface layer. The intermediate reinforcing layer isformed from three-dimensional cross-linked polyurethane in the form of athin elastic film. Additionally, woven fabrics or mats made from suchmaterials as fiberglass have been used as reinforcing layers. U.S. Pat.No. 4,130,614, issued Dec. 19, 1978 to G. E. W. Saidla, discloses astructural foam article formed by pouring a polyurethane resin onto afiber-reinforcing sheet that is placed over a facing sheet in a mold.The polyurethane resin foams through the fiber-reinforcing sheet andbonds to the facing sheet, resulting in a structural foam article havinga polyurethane resin core bonded to a facing sheet with an intermediatelayer formed from the fiber-reinforcing sheet and polyurethane resin.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a method offorming a reinforced plastic skin for an automobile interior trimstructure, comprising the steps of supplying a plastic material onto amold surface defining the outer surface of the interior trim structure,heating the plastic material to fuse the plastic material into a unitarylayer thereof, embedding a reinforcing material into the layer, andcooling the plastic material and the reinforcing material. Thereinforcing material can be a woven mesh of, for example, fiberglass.The plastic is preferably a polyvinyl chloride. The woven fiberglassfabric can be embedded into the layer by pressing it into the backside(i.e., non-decorative side) of the plastic layer. Alternatively, thewoven mesh can be embedded by placing it onto the layer, supplying anadditional amount of the plastic material over it and the layer, andheating the plastic material to fuse the plastic material together,whereby a single layer of plastic material is formed having the wovenmesh embedded therein.

The reinforcing material need not extend over the entire area of theouter skin. It can be located wherever reinforcement of the outer skinis desirable. Preferably, however, the reinforced outer skin is formedas a part of producing an air bag door cover that is unitary with theremainder of the outer skin of the interior trim structure. Accordingly,the method preferably further includes the steps of incorporating a tearseam into the layer, and embedding the woven mesh into the layer suchthat it surrounds the tear seam. That is, the woven mesh is locatedabout the tear seam, but does not overlie it. Preferably, the woven meshcovers the air bag door cover and extends into the surrounding area ofthe outer skin.

In accordance with another aspect of the invention, a method is providedfor forming a reinforced air bag door cover as a unitary part of anouter skin for an automobile interior trim structure. This methodincludes the steps of supplying a plastic material onto a mold surface,heating the plastic material to fuse the plastic material into a unitarylayer thereof, defining a portion of the layer that corresponds to atear seam for the air bag door cover, embedding a reinforcing materialinto the layer such that the reinforcing material surrounds the portion,and cooling the plastic material and the reinforcing material. Thereinforcing material preferably comprises a woven mesh of fiberglass andthe plastic material preferably comprises a polyvinyl chloride.

A gap having a shape that generally corresponds to the tear seam portioncan be formed in the woven mesh prior to the embedding step.Alternatively, the woven mesh can be scored or otherwise separated alongthe tear seam portion after being placed onto the layer of plasticmaterial. Moreover, the tear seam can be formed by scoring, engraving,embossing, or otherwise prior to embedding the woven mesh into the layerabout the tear seam.

The reinforcing material is preferably embedded into the plastic layerin either of two ways. One way includes forming the layer of plasticmaterial such that it has a first side in contact with the mold surfaceand a second side located opposite the first side and then pressing thereinforcing material into the second side of the layer. Preferably, awoven mesh having interstices therein is pressed into the plastic layersuch that plastic material extends into the interstices. The result is areinforcing layer that is securely embedded into the plastic outer skin.

A second way of embedding the reinforcing material includes placing thereinforcing material onto the layer, supplying an additional amount ofthe plastic material over the reinforcing material and the layer, andheating the plastic material to fuse the plastic material together,whereby a single layer of plastic material is formed having thereinforcing material embedded therein. Again, a woven mesh havinginterstices is preferably used such that the plastic fuses through theinterstices during the heating step.

In accordance with yet another aspect of the present invention, there isprovided an outer skin for an automobile interior trim structure havingan air bag door cover incorporated therein. The outer skin comprises alayer of plastic material having a first surface defining an exposeddecorative surface and a second surface having a tear seam therein thatdefines at least one air bag door cover. The outer skin includes areinforcing material which is embedded in the layer below the firstsurface and which extends over the air bag door cover on either side ofthe tear seam. As in the other embodiments of the invention, thereinforcing material preferably comprises a woven mesh havinginterstices therein. Accordingly, the plastic material preferablyextends into the interstices to securely embed the woven mesh into theplastic layer. The woven mesh or other reinforcing material can beembedded into the backside of the plastic layer or can be completelyencased within the plastic layer.

The reinforcing material is located on either side of the tear seam andpreferably covers the portion of the layer plastic that acts as the airbag door cover. Even more preferably, the reinforcing material extendsinto the area of the layer immediately surrounding the air bag doorcover and tear seam. The reinforcing material located about the tearseam helps insure rapid, accurate separation of the air bag door coveralong its designated tear seam upon deployment of the air bag. Moreover,the reinforcing material provides additional structural integrity to theair bag door that overlies the air bag deployment opening.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred exemplary embodiments of the present invention willhereinafter be described in conjunction with the appended drawings,wherein like designations denote like elements, and:

FIG. 1 is a perspective view of an interior trim structure having anouter skin of the present invention that includes a unitary air bag doorcover;

FIG. 2 is a cross-sectional view taken along the 2--2 line of FIG. 1 andshowing a section of woven fiberglass mesh embedded in the outer skin inaccordance with the invention;

FIG. 3 is an enlarged view of a designated portion of the cross-sectionshown in FIG. 2;

FIG. 3A is an enlarged view as in FIG. 3, but which shows an alternativearrangement for embedding the woven mesh into the outer skin;

FIG. 4 is a fragmentary top view of a woven mesh suitable for use in theinvention; and

FIGS. 5 through 8 depict a diagrammatical representation of a moldsuitable for practicing the method of the present invention.

It should be understood that the various figures are for purposes ofillustration only and are primarily diagrammatic rather than pictorial.They are not intended to represent scaled views of the structures thatthey depict.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 depict an automobile interior trim structure and, inparticular, a portion of a dashboard 10 that includes a pair of integralair bag doors 12. Dashboard 10 is formed from three layers--an outerskin 14, an intermediate foam layer 16, and a rigid insert 18. Outerskin 14 has an exterior surface 20 which is exposed to the automobileoccupants when dashboard 10 is assembled as a component part of anautomobile. As described below in greater detail, air bag doors 12 aredefined by hinged portions of insert 18 and a tear seam 22 formed in thebackside of outer skin 14. Upon a collision being detected by a sensor24, a gas generator 26 inflates an air bag 28 which forces the hingedportions of insert 18 outwardly, thereby tearing foam layer 16 and outerskin 14 along tear seam 22.

Outer skin 14 and insert 18 are typically preformed and can thereafterbe co-molded together by foam layer 16. Outer skin 14 can be a polyvinylchloride, such as plastisol or drysol, or anacrylonitrile-butadiene-styrene (ABS) resin and the details of itsconstruction will be described below in greater detail. Insert 18 can bepreformed as described, for example, in U.S. Pat. No. 4,734,230, issuedMar. 29, 1988 to R. D. Rhodes, Jr. et al. The preformed outer skin 14and insert 18 can then be placed on opposing inner surfaces of a moldand bonded together by the formation of foam layer 16 therebetween. Sucha process is described in U.S. Pat. No. 4,743,188, issued May 10, 1988to J. D. Gray et al. Other means of forming foam layer 16 and insert 18and bonding them to outer skin 14 are known to those skilled in the artand can be suitably employed to produce dashboard 10.

Referring now to FIG. 3, dashboard 10 includes an air bag deploymentopening defined by air bag doors 12 formed as a part of insert 18 andpivotable about a pair of hinges 30. The portion of outer skin 14 thatincludes tear seam 22 and that overlies doors 12 comprises an air bagdoor cover 32 for the air bag deployment opening. Cover 32 includes tearseam 22 which is defined by a reduction in thickness of cover 32.

In accordance with the present invention, cover 32 of outer skin 14includes a woven fiberglass mesh 34 embedded in the backside 36 thereof.A gap 38 is provided in mesh 34 to accommodate tear seam 22. As will beunderstood by those skilled in the art, mesh 34 reinforces cover 32 andrestricts elongation of cover 32 upon deployment of air bag 28. As aresult, the likelihood of cover 32 becoming separated from foam layer 16is reduced and, therefore, the likelihood of undesirable fragmentationof foam layer 16 is reduced. Also, less elongation of cover 32 should beaccompanied by faster rupturing of tear seam 22. Moreover, thereinforcement provided by mesh 34 acts to insure that cover 32 separatesalong the designated tear seam, thereby helping to insure properdeployment of air bag 28.

Although mesh 34 is shown extending beyond the surface of backside 36,it will be appreciated that mesh 34 can be flush with or slightlyrecessed into backside 32 without departing from the scope of thepresent invention. Referring now to FIG. 4, mesh 34 preferably has aweave of strands 40 that are spaced sufficiently to provide interstices42 into which extends the material (e.g., PVC or ABS) that makes upouter skin 14. This arrangement helps bond mesh 34 to cover 32 and isbelieved to help restrict elongation of cover 32 upon expansion of airbag 28.

Mesh 34 preferably surrounds tear seam 22. That is, mesh 34 ispreferably located about tear seam 22, but does not overlie it andtherefore does not interfere with the separation of air bag doors 12during deployment of air bag 28. In a highly preferred embodiment, mesh34 is located throughout air bag door cover 32 and extends into thesurrounding area of outer skin 14, as indicated by the dashed line 44shown in FIG. 1.

Tear seam 22 is preferably formed in backside 36 of cover 32. Asindicated in FIG. 1, tear seam 22 is therefore not visually observableby the automobile occupants. Other means of pre-weakening cover 32 toform a tear seam therein can of course be used without departing fromthe scope of the present invention. Moreover, it is believed that if thethickness of the portion of cover 32 bridging gap 38 is madesufficiently small, then the structural integrity provided by mesh 34would be enough to separate cover 32 at gap 38 without the need forpre-weakening of cover 32. In the illustrated embodiment, tear seam 22comprises an H-shaped portion of cover 32. It will of course beunderstood that tear seams utilizing other shapes (e.g., C, U, or X) canbe selected and that a gap corresponding to the selected shape would beprovided in mesh 34.

Referring now to FIG. 3A, an alternative embodiment of dashboard 10 ofFIG. 3 includes substantially the same construction as that shown inFIG. 3. However, this embodiment includes a woven mesh 34' that iscompletely embedded, i.e., encased, within a cover 32' that is a unitarypart of an outer skin 14'. Preferably, woven mesh 34' has the sameconstruction as that of mesh 34 (i.e., as shown in FIG. 4) so that thematerial that forms cover 32' is fused through the interstices in mesh32'.

In conjunction with FIGS. 5 through 8, there will now be described amethod for forming outer skin 14 with mesh 34 embedded therein. FIG. 5shows a mold assembly 50 that includes a mold form 52 and a charge box54. Mold 52 includes a surface 56 which is used to produce exteriorsurface 20 of outer skin 14. Mold surface 56 thus has a shape thatcorresponds to the desired geometry of the finished reinforcing preform.Mold surface 56 can be textured and otherwise engraved to provideexterior surface 20 with grain effects and other aesthetically pleasingdetailing. Charge box 54 is partially filled with a charge of powderedthermoplastic material 58 out of which outer skin 14 is to be made.Thermoplastic material 58 can be a dry resin powder material withsuitable coloring and plasticizer content, such as described in U.S.Pat. No. 4,923,657 issued May 8, 1990 to J. C. Gembinski et al.

Mold 52 mates with charge box 54 such that surface 56 of mold 52 is inopen communication with the contents of charge box 54. Mold assembly 50further includes a clamp or clamps 60 which secure and seal mold 52 tocharge box 54 to prevent thermoplastic material 58 from escapingtherebetween. When clamped together, mold 52 and charge box 54 form asealed mold chamber.

Initially, mold form 52 is placed in an inverted position and clamped tocharge box 54, as described above. Mold 52 is then heated to asufficient temperature to cause approximately one millimeter of drypowder to attach and fuse. Mold assembly 50 is then rotated 180° to theposition shown in FIG. 6 to thereby dump thermoplastic material 58against surface 56. To effect this rotation, mold assembly 50 isrotatably supported by a suitable drive 62, such as that described inU.S. Pat. No. 4,664,864, issued May 12, 1987 to J. M. Wersosky, herebyincorporated by reference.

Since mold surface 56 has been heated, a layer 64 of material 58attaches to surface 56 and fuses together. The remaining material 58 isdumped back into charge box 54 by rotating mold assembly 50 back to itsinitial position, as shown in FIG. 7. Mold form 52 and charge box 54 arethen disconnected. While plastic layer 64 is still at an elevatedtemperature and is still in a substantially liquid state, woven mesh 34is embedded into plastic layer 64 by pressing the mesh 34 into theexposed surface of layer 64. Preferably, this is done such that theplastic material of layer 64 extends into the interstices of mesh 34. Ifnecessary, mold 52 can then be heated more to cure the thermoplasticmaterial together. Finally, mold 52 is cooled to solidify layer 64together which then comprises outer skin 14. U.S. Pat. No. 4,562,025,issued Dec. 31, 1985 to J. D. Gray, hereby incorporated by reference,provides more specific information on casting thermoplastic material.

If the outer skin formed by the above-described method is to include airbag door cover 32, then tear seam 22 can be added as an additional stepand woven mesh 34 is placed on layer 64 such that it surrounds tear seam22 (i.e., it forms gap 38 at tear seam 22). Tear seam 22 can be added tolayer 64 in any manner. For example, tear seam 22 could be molded intolayer 64 prior to embedding mesh 34 therein. Alternatively, tear seam 22could be added after mesh 34 is embedded in layer 64. In a like manner,gap 38 can be formed in mesh 34 prior to embedment thereof, or,alternatively, by scoring mesh 34 after its attachment to layer 64. Thislatter means of forming gap 38 could be accomplished simultaneously withthe formation of tear seam 22. That is, once formed, cover 32 could bescored in an operation that simultaneously separates mesh 34 to form gap38 and scores layer 64 to form tear seam 22. Preferably, mesh 34 isspaced from tear seam 22 by approximately 1/4 of an inch so that gap 38is about 1/2 of an inch wide.

In accordance with another aspect of the present invention, outer skin14', which includes cover 32' of FIG. 3A, can be formed by a modifiedversion of the method described above. Initially, a layer 64' ofthermoplastic material 58 is formed as described above in connectionwith FIGS. 5 through 7. Then, woven mesh 34' is placed on the exposedside of layer 64'. This can either be done by embedding mesh 34' intolayer 64', as described above, or by allowing layer 64' to cool to asolid or semi-solid state and thereafter placing mesh 34' thereon. Mold52 is then re-clamped to charge box 54 and mold assembly 50 is theninverted again to dump another charge of material 58 onto layer 64' andmesh 34'. A second layer 66' is thereby formed. Mold assembly is rotatedonce more to return it to its initial position, as shown in FIG. 8.Layers 64' and 66' are thereafter heated to completely fuse them into asingle, unitary layer of plastic material that encases mesh 34'.

Rather than reattaching mold 52 to charge box 54 and dumping thematerial 58 onto layer 64', a plastic material in either dry or liquidform could be sprayed over mesh 34' to form a single layer of materialthat encases mesh 34'. More generally and as will be understood by thoseskilled in the art, outer skins 14 and 14' can be formed using othercasting systems, such as a spray system. A slush process suitable foruse in carrying out the method of the present invention is described inU.S. Pat. No. 4,623,503, issued Nov. 18, 1986 to E. Anestis et al.

It will thus be apparent that there has been provided in accordance withthe present invention a reinforced outer skin for an automobile interiortrim structure, as well as a method for making the same, which achievesthe aims and advantages specified herein. It will of course beunderstood that the foregoing description is of preferred exemplaryembodiments of the invention and that the invention is not limited tothe specific embodiments shown. Various changes and modifications willbecome apparent to those skilled in the art. For example, instead of awoven mesh or other integral reinforcing sheet, individual fibers orreinforcing particles could instead be used to reinforce the outer skin.Such fibers or particles could, for example, be applied with a binder orcould be forced into the layer of plastic material before it is allowedto solidify. Other variations will become apparent to those skilled inthe art and all such variations and modifications are intended to comewithin the spirit and scope of the appended claims.

We claim:
 1. A method for forming a reinforced air bag door cover as aunitary part of an outer skin for an automobile interior trim structure,comprising the steps of:supplying a plastic material onto a moldsurface, heating said plastic material to fuse said plastic materialinto a unitary layer thereof, defining a portion of said layer thatcorresponds to a tear seam for the air bag door cover, embedding areinforcing material into said layer such that said reinforcing materialsurrounds said portion, and cooling said plastic material and saidreinforcing material.
 2. The method of claim 1, wherein said reinforcingmaterial comprises a woven mesh and wherein the method furthercomprises, prior to said embedding step, the step of forming in saidwoven mesh a gap having a shape that generally corresponds to saidportion.
 3. The method of claim 1, wherein said reinforcing materialcomprises a woven mesh and wherein said embedding step comprises:placingsaid woven mesh onto said layer over said portion, and scoring saidwoven mesh along said portion.
 4. The method of claim 1, furthercomprising the step of forming the tear seam in said layer of plasticmaterial prior to said embedding step.
 5. The method of claim 1, whereinsaid layer of plastic material is formed such that it has a first sidein contact with said mold surface and a second side located oppositesaid first side and wherein said embedding step further comprisespressing said reinforcing material into said second side of said layer.6. The method of claim 5, wherein said pressing step further comprisespressing a woven mesh having interstices therein into said second sideof said layer such that said plastic material extends into saidinterstices.
 7. The method of claim 1, wherein said embedding stepfurther comprises:placing said reinforcing material onto said layer,supplying an additional amount of said plastic material over saidreinforcing material and said layer, and heating said plastic materialto fuse said plastic material together, whereby a single layer ofplastic material is formed having said reinforcing material embeddedtherein.
 8. The method of claim 7, wherein said reinforcing materialcomprises a woven mesh having interstices therein and wherein saidheating step further comprises heating said plastic to a temperaturesufficient to permit said plastic to fuse through said interstices. 9.The method of claim 1, wherein said plastic comprises a polyvinylchloride and said reinforcing material comprises fiberglass.
 10. Amethod of forming a reinforced plastic skin for an automobile interiortrim structure, comprising the steps of:supplying a plastic materialonto a mold surface defining the outer surface of the interior trimstructure, heating said plastic material to fuse said plastic materialinto a unitary layer thereof wherein said unitary layer has margins,embedding a reinforcing material into said layer by placing a woven meshonto said layer at a location intermediate the margins of said layer,supplying an additional amount of said plastic material over said wovenmesh and said layer, and heating said plastic material to fuse saidplastic material together, whereby a single layer of plastic material isformed having said woven mesh embedded therein, and cooling said plasticmaterial and said reinforcing material.
 11. A method of forming areinforced plastic skin for an automobile interior trim structure,comprising the steps of:supplying a plastic material onto a mold surfacedefining the outer surface of the interior trim structure, heating saidplastic material to fuse said plastic material into a unitary layerthereof, incorporating a tear seam into said layer, embedding areinforcing material into said layer such that said reinforcing materialsurrounds said tear seam, and cooling said plastic material and saidreinforcing material.